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LinuxCVE-2024-26960

HistoryMay 01, 2024 - 6:15 a.m.

CVE-2024-26960

2024-05-0106:15:12

CWE-362

Linux

web.nvd.nist.gov

linux kernel

vulnerability

swap functionality

race condition

memory access

CVSS3

5.5

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

AI Score

6.4

Confidence

Low

EPSS

Percentile

10.3%

JSON

In the Linux kernel, the following vulnerability has been resolved:

mm: swap: fix race between free_swap_and_cache() and swapoff()

There was previously a theoretical window where swapoff() could run and
teardown a swap_info_struct while a call to free_swap_and_cache() was
running in another thread. This could cause, amongst other bad
possibilities, swap_page_trans_huge_swapped() (called by
free_swap_and_cache()) to access the freed memory for swap_map.

This is a theoretical problem and I haven’t been able to provoke it from a
test case. But there has been agreement based on code review that this is
possible (see link below).

Fix it by using get_swap_device()/put_swap_device(), which will stall
swapoff(). There was an extra check in _swap_info_get() to confirm that
the swap entry was not free. This isn’t present in get_swap_device()
because it doesn’t make sense in general due to the race between getting
the reference and swapoff. So I’ve added an equivalent check directly in
free_swap_and_cache().

Details of how to provoke one possible issue (thanks to David Hildenbrand
for deriving this):

–8<-----

__swap_entry_free() might be the last user and result in
“count == SWAP_HAS_CACHE”.

swapoff->try_to_unuse() will stop as soon as soon as si->inuse_pages==0.

So the question is: could someone reclaim the folio and turn
si->inuse_pages==0, before we completed swap_page_trans_huge_swapped().

Imagine the following: 2 MiB folio in the swapcache. Only 2 subpages are
still references by swap entries.

Process 1 still references subpage 0 via swap entry.
Process 2 still references subpage 1 via swap entry.

Process 1 quits. Calls free_swap_and_cache().
-> count == SWAP_HAS_CACHE
[then, preempted in the hypervisor etc.]

Process 2 quits. Calls free_swap_and_cache().
-> count == SWAP_HAS_CACHE

Process 2 goes ahead, passes swap_page_trans_huge_swapped(), and calls
__try_to_reclaim_swap().

__try_to_reclaim_swap()->folio_free_swap()->delete_from_swap_cache()->
put_swap_folio()->free_swap_slot()->swapcache_free_entries()->
swap_entry_free()->swap_range_free()->
…
WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries);

What stops swapoff to succeed after process 2 reclaimed the swap cache
but before process1 finished its call to swap_page_trans_huge_swapped()?

–8<-----

Affected configurations

Vulners

Node

linuxlinux_kernelRange4.11–5.10.215

linuxlinux_kernelRange5.11.0–5.15.154

linuxlinux_kernelRange5.16.0–6.1.84

linuxlinux_kernelRange6.2.0–6.6.24

linuxlinux_kernelRange6.7.0–6.7.12

linuxlinux_kernelRange6.8.0–6.8.3

linuxlinux_kernelRange6.9.0≥

VendorProductVersionCPE
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

Vendor	Product	Version	CPE
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "mm/swapfile.c"
    ],
    "versions": [
      {
        "version": "7c00bafee87c",
        "lessThan": "d85c11c97ecf",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "7c00bafee87c",
        "lessThan": "2da5568ee222",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "7c00bafee87c",
        "lessThan": "1ede7f1d7eed",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "7c00bafee87c",
        "lessThan": "0f98f6d2fb5f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "7c00bafee87c",
        "lessThan": "3ce4c4c653e4",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "7c00bafee87c",
        "lessThan": "363d17e7f790",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "7c00bafee87c",
        "lessThan": "82b1c07a0af6",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "mm/swapfile.c"
    ],
    "versions": [
      {
        "version": "4.11",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "4.11",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.215",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.154",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.1.84",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.24",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.7.12",
        "lessThanOrEqual": "6.7.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8.3",
        "lessThanOrEqual": "6.8.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.9",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]